This invention broadly relates to methods for delineating individual thin film magnetic head arrays from a substrate and, more particularly, to a high yield, reproducible delineation method which results in precise, well-defined gap regions and which is readily adapted to cost effective batch processing.
The development of thin film magnetic head arrays has become the subject of increased interest, especially in the area of high speed, high density recording (and retrieval) of digital computer information on magnetic media (tapes, disks). Thin film magnetic head arrays, because they can be fabricated using modified versions of the batch processing technolgies employed by integrated circuit manufacturers offer a number of distinct advantages over conventional (wire-wound, ferrite core) magnetic heads. Such advantages include: (1) cost-effective manufacture of high density multi-element arrays with precise head geometries and dimensional tolerances, since thin film deposition and photolithographic technologies are utilized; (2) potential for improved frequency response (due to material and geometry) and a more precise "track" definition (due to sharper field gradients); (3) potential for better head-to-head uniformity and increased reliability; and (4) potential for totally (or partially) integrated addressing electronics, again resulting in lower costs, high speed, and better reliability.
Known methods for fabricating thin film magnetic head arrays typically consist of sequentially depositing thin film layers of magnetic, conductive, and insulative materials. The magnetic thin film layers (usually Permalloy) form the magnetic yoke of the head structure and serve the function of concentrating magnetic flux according to desired geometries. The conductor thin film layer, typically gold or copper, form the "turns" or windings around the magnetic yoke of the individual heads which induce a magnetic field when current is passed through them. The delineated layer of conductive thin films also provides electrical interconnection between the coil section of the heads and the power supply/addressing network which is used to activate the array. Finally, insulator thin film layers (polyimides, SiO.sub.2) are used to electrically isolate the various thin film conductor layers (especially in multi-turn head designs), as well as to provide precise gap spacing between upper and lower layers of the magnetic yoke. The various thin film layers are typically deposited by a variety of techniques including vacuum deposition (sputtering, evaporation), electroplating, and spin-coating (e.g., for spin-on insulator materials). The resultant multi-layer thin film array structure is fabricated on a rigid substrate (e.g., silicon wafer), and the thin film layers are delineated into patterns (as required) using photolithographic masking and wet chemical or plasma etching techniques. A completed thin film magnetic head array typically consists of anywhere from a few to several hundreds of individual heads (at densities of 50-300 heads per inch), and can vary from a few tenths of an inch to several inches in length. Multiple arrays (or array modules) are processed simultaneously on a given substrate, and many substrates are processed together so that cost advantages of batch fabrication are realized.
The vast majority of the known thin film magnetic head structures utilize the so called vertical configuration in which the gap length is perpendicular to the plane of the substrate, as illustrated in FIG. 2. The presence of the substrate in the recording plane makes this structure resistant to wear and scratches. Achieving this wear resistance, however, requires that the arrays of heads be precisely delineated from the substrate in order to complete the array fabrication cycle. In the known processes, this delineation of individual arrays from the silicon wafer substrate is accomplished by a dice and lap procedure. The dicing operation is usually performed with a high speed microelectronic dicing saw using thin diamond impregnated cutting wheels. Although such equipment is capable of accurate delineation of wafer substrates and leaves relatively smooth surfaces on the cut edges, smearing of the thin film layers, edge chipping and some degree of cut-edge surface roughness are always present. To make the heads operational, the individual arrays must then be edge-lapped to achieve the desired surface finish and thin film definition in the gap region (generally designated 16 in FIG. 2). This lapping/polishing process is particularly undesirable for the following reasons: ( 1) it is not a "batch" process, since arrays typically must be mounted and lapped individually, or at best, a few at a time with elaborate fixturing; (2 ) the process is extremely operator dependent since each array must be manually aligned and mounted to precise tolerances, then sequentially lapped through a series of grit sizes to achieve the desired result. End point of the process and uniformity of the process across long arrays are typically difficult parameters to control. Hence, the procedure is time consuming and may not yield consistent results; (3) the arrays are subject to much handling and potential mechanical abuse during both the dicing and lapping processes, contributing to low device yields. Such a low yield process step near the end of a fabrication cycle is particularly costly since much time and effort has typically been expended on the device to arrive at this point; and (4) the array edge-lapping process is not one that can be easily automated to high volume manufacturing levels at which the unit cost of batch process devices can be very low.
Accordingly, there exists a need for an alternative method of thin film magnetic head array delineation which will provide cost effective batch processing, while simultaneously assuring precise recording gap definition and high yields.